1. Field of the Invention
The present invention relates to novel hydrophobic, spheroidal, precipitated silica particulates, and to a process for the preparation thereof and its use as reinforcing filler material in silicone elastomers.
2. Description of the Prior Art
It is known to this art to use pyrogenic silica, in particular, as a reinforcing filler in hardenable organopolysiloxane compositions. However, pyrogenic silica has the disadvantage of being quite expensive.
This art has long sought to replace, at least in part, pyrogenic silica with the lower cost precipitated silica. Various processes have to date been proposed for the preparation of precipitated silica. These, however, are quite complex and entail the careful control of temperature, reagent concentration, pH values, and the like. Compare French Patent No. 1,352,354.
Attempts have also been made to improve the reinforcing properties of precipitated silica for silicone applications, by rendering the silica hydrophobic by means of an appropriate surface treatment (for example, by the use of silanes or silazanes). Hydrophilic silica materials rendered hydrophobic by such a treatment and suitable for silicone applications are described in French Patent No. 2,356,596.
These precipitated silicas may have advantageous properties; nonetheless, they may still prove to be insufficient in relation to their dielectric properties which are important for certain specific applications, such as cables.
Finally, in a general manner the incorporation of silica into silicones presents certain other problems. In effect, this incorporation is carried out in low shear mixers. For the proper introduction of the silica into the silicone paste, the silica must have a sufficient density.
On the other hand, it is advantageous to have a product that may be handled easily, which in this case implies good flowability.